QByteArray not initializing

[mzimmers]

@mrjj I'm appending a character at a time:

    uint8_t c;
    n = strlen(mac);
    for (uint32_t i = 0; i < n; i +=2)
    {
        p = mac + i;
        sscanf(p, "%2x", (int *) &c);
        qMac.append((char) c);
    }

I wonder if it's objecting to the content of my characters?

The behavior is unpredictable; sometimes I get this error instead of a segmentation fault:

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

[mrjj]

@mzimmers said in QByteArray not initializing:

std::bad_alloc'

that is normally for an out of memory situation ?

the crash could be from sscanf.
also i think you can go out of bounds with this code
n = strlen(mac);
for (uint32_t i = 0; i < n; i +=2)

if n is not even and you increase with 2 would that not count wrongly ?

[mzimmers]

@mrjj everything you say is true, but it's not crashing on the sscanf() call. And it's not getting far enough into the mac string to overrun. I'm doing the identical thing with 2 other QByteArrays before this one, and they work perfectly.

I even thought there might be something wrong with my variable name, so I refactored...same thing.

[mranger90]

Without seeing the rest of the code, I would guess that something in that method is blowing the stack.
Look for a buffer overrun.

[mrjj]

@mzimmers
Hmm. if you single step the loop, cant you see what is wrong when
it crashes ?

you do the same thing with qText and qKey?

[mzimmers]

@mrjj here's the code in its entirety:

#include <QByteArray>
#include <QDebug>
#include <QCoreApplication>
#include <QMessageAuthenticationCode>
#include <QCryptographicHash>

int test(char *key, char *txt, char *mac);

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    char  Key8[] =          "60e431591ee0b67f0d8a26aacbf5b77f"  //  arbitrary key
                            "8e0bc6213728c5140546040f0ee37f54";
    char  Txt8[] =                                              //  Len = 1054 BYTES
                "e5098b6a0b1cfc57c6a76537104a39c48baecb15c6bbb46fbb0b745f9c9e5c05"
                "cfcfabb33786f7b7b5b0ce74eeec9eb84f87d2494fab3ec1f4d3bd9c99821890"
                "ee352a1d40964264fbf2c93c6ded2583cc75dcb27bf4fdb489cabcf97bfa5cc6"
                "4b2352cfb0b3a707a0579eb713b697cd0b5e3377d1feb9f181d7b89cc86dee4f"
                "ed8269f10e44ec48adc6940c6badbb40122c1dc2d9323920e4e1fbad0b4397d4"
                "dc38b8ade3b3dace2926f464fa3b5b82ebc5e3b81cf647e8bbd2cb55c9e31ffd"
                "212f8729b66739421c6106e64ac83d3b9e13cd8321b3a9f10d9171bb8cb74e71"
                "c34d1e8d0fc8d14b8e5e12bbe2bd2a1431fc224b70d228e4e2063509db26ecd9"
                "ca7cc402763e69928805600a4a80eab4ae6a2c3792b98c6942195e643f98c0dc"
                "3fa3c2b07431cbbe113e38fc0b7b45c51c4431700ed29d2736b236f63f759323"
                "29aa60be9009bd7832f1e1b9ac1503ec84727a1e6c8423c7c5b903e763262d55"
                "9078e654532e0868f206a468b5b5ebd3eddb4f673536e5f0f8160e5f3311561b"
                "7cf79c9c440974355965c931aec5c7225f69f776f052ac4bd6b19f85389fd61d"
                "f60ecabbeb00c8886ff7983d20ac5d81e303bc71253f40806772fd81f9387402"
                "05a5b7dcd07cce083da258b493d275967f91e4815d656936b342727cfe45f973"
                "b2a5ac257ce64c5eca4f53be8d9fd90c3dfcb8cd1e2cef15c307449ed02c2e17"
                "04f4f1be76a40b311ee7cf81987b5089252a807ef3fc99c79eabbc0ef657d897"
                "037bced04620d32a425015283bcea1b53e0484bb613d30f14c1422f5f82cc29a"
                "b7228b8375c06bf13d746dd9ff00953a90720badf2577d3ed62cbe7a5f15b3c9"
                "29d26ffe8aee9d2d17391ebc6a79f4bd235d5f7b2db2455343d9d7c6b27972cc"
                "6071c36a0d112f86d98972fb06a186e900abc64e9ab653db9b05b70079c0c84a"
                "64e8cfee8690eaa68a4bafbb5be112632e46894ec2cc6e7ce697a4513d517deb"
                "3e20dbb37ed5963232671e27ef9f62d6b514f0a22c5a5dde2d77e7e184965958"
                "f5002fe17d47fbd5d9c407644d443ce89eff427360cae9aa788dc8d7d9f62439"
                "916f139f094ee035884cb29dfa396941f0eec9e8e782da88cdc18e5bc1d9a535"
                "1b57ce15ac520ffa47e666f87fe5b18ab3c8cb2a48ecf81f36fb8397c6a7a5f5"
                "9a9fa96cedbb4ecd1c7a6d9d65afdb6bef7791600b6e0a18ba23edb06fc9ec21"
                "162feccc54f2665611f10db53401b18bade263b3b972da1a612115d144a54260"
                "97efdf5c6a5d1f3c2d318f687242f993f5f1884bd95f2ece34dd4320cea46f5a"
                "26c7c945b665402778233bdda9d97c2acd8c4a4ff39dcfdc3a3fbfc5942e3ab8"
                "ca9ff4aec17293c1fbaf583d603002f93f9befe8909485eb7c30d0e91fac6c22"
                "8c5fa6c011eddeafbdbe30af20ae53a85206c03d37ac17a30096bfb4f584cd3f"
                "72ef28a3303cea9cc636095c70bb36de0eb50577704d4faed05bd54da020";

    char  Mac8[] =                          //  HMAC_SHA256 7.3728=410ms 18.4320=
                "4a0ce2f8ffca9e77443e661c88ccdc04ba6ac9bb901642fadae7fe8e4c2d50f7";

    test(Key8, Txt8, Mac8);
    return a.exec();
}

int test(char *key, char *txt, char *mac)
{
    QByteArray qKey;
    QByteArray qTxt;
    QByteArray qMac;
    uint8_t c;
    char *p;
    uint32_t n;

    n = strlen(txt);
    for (uint32_t i = 0; i < n; i += 2)
    {
        p = txt + i;
        sscanf(p, "%2x", (int *) &c);
        qTxt.append((char) c);
    }

    n = strlen(key);
    for (uint32_t i = 0; i < n; i +=2)
    {
        p = key + i;
        sscanf(p, "%2x", (int *) &c);
        qKey.append((char) c);
    }

    n = strlen(mac);
    for (uint32_t i = 0; i < n; i +=2)
    {
        p = mac + i;
        sscanf(p, "%2x", (int *) &c);
        qMac.append((char) c);
    }

    QMessageAuthenticationCode auth(QCryptographicHash::Sha256, qKey);
    auth.addData(qTxt, 1054);
    qMac = auth.result();

    return (strcmp(qMac.data(), mac) == 0);
}

qTxt and qKey work perfectly.

EDIT:

I'm aware that the strlen calls might not work right all the time, but they seem to be OK in this example. There's something wrong with my qMac variable, at least in the eyes of the debugger.

[mrjj]

super, let me crash it ;)

[aha_1980]

@mzimmers: Your problem with Mac8 is most likely that the array has an unequal number of chars...

PS: I already said in your other thread that you can use QByteArray::fromHex().

[mzimmers]

@aha_1980 not sure what you mean by "an unequal number of chars".

I saw your other response, but didn't understand it. I'll take another look.

[aha_1980]

@mzimmers said in QByteArray not initializing:

@aha_1980 not sure what you mean by "an unequal number of chars".

strlen(Mac8) == 65

Your loop is iterating with steps of two. So you're reading over the end of Mac8 with sscanf().

I'm not sure what QByteArray::fromHex() will do with this invalid input, but most likely it will not crash. (If it does, we create a bugreport).

[mzimmers]

@aha_1980 this crash is occurring on the second iteration through the loop, so I don't think it's an array/string overrun.

[mrjj]

Oddly enough i dont crash here
it just converts to 32 values each time.

[mrjj]

@mzimmers
Hi
Can you try
// QCoreApplication a(argc, argv);
// a.exec();
and just return 0;

You are not sending it a close signal so i think crash is due to killing it with debugger.

At least i cannot crash it without running the coreapp and exec().

[mzimmers]

@mrjj yeah, I'm pretty sure my loops are OK. I honestly don't know what's going on -- maybe some weird bug in the constructor.

I removed the core app stuff...same results.

I think I'll implement aha_1980's suggestion. I took another look, and it's a lot simpler than this. I'll report back on how I do with it.

[mrjj]

@mzimmers
Ok. i checked the loop and its 64 in length and result is 32 in bytearray.
no crashes at any time.
Very odd then.
Im on 64 bit.

[mzimmers]

I'm on Windows 10, using MinGW, FWIW. Just tried null terminating the string myself, and still bombs in the loop (though aha's suggestion works).

[mrjj]

@mzimmers
Hmm visual studio here.
Maybe its related to mingw.
I will try tomorrow at work with mingw and see.
I dont like when crashes are not reproducible.

[JonB]

@mzimmers said in QByteArray not initializing:

@mrjj here's the code in its entirety:

uint8_t c;

sscanf(p, "%2x", (int *) &c);

c holds a 8-bit int, right? Firstly that's not right for (int *) &c, and secondly look at sscanf("%2x", it will expect the address of a whole int (32-bit? 64-bit?) to store its result. So you're overwriting the local stack space, hence possible crashing? Or, uint8_t is allocated on an odd address boundary, which won't be good.

Make c be a proper int, or fix your sscanf.

Your understanding of QByteArray is fine, but not of scanf :-)

Also, if you use QByteArray::fromHex(), you won't need to use sscanf :)

[mzimmers]

@JNBarchan the pointer should be OK, as far as I can see. Your point about the sscanf() overwriting the output buffer may be valid, though it's really odd that the first two loops worked fine.

[mrjj]

@JNBarchan
Thats a really good observation and might explain why
no crashing here 64bit. Completely overlooked it :)